Specific radio frequency bands are set aside for wireless cellular communications by spectrum regulatory authorities (such as the Federal Communications Commission in the United States of America) to ensure the reliable operation of cellular communication systems, and are referred to as cellular bands. The term ‘spectrum’ is commonly used to refer to the aggregate bands that are assigned to the cellular communication network, also referred to as the cellular communication system, in any given jurisdiction. Another analogous phrase to spectrum is radio frequency resources.
Cellular bands can be contiguous or non-contiguous and are typically divided into sub-bands, which again can be contiguous or non-contiguous, that are licensed to mobile network operators. A mobile network operator thus deploys the network infrastructure of a cellular communication system, typically comprising a Radio Access Network (RAN) and a Core Network (CN), upon obtaining a spectrum utilization license, i.e. a license to use a particular cellular band or sub-band. Connection of User Equipment (UE) to system radio Access Points (AP) of the network infrastructure is facilitated by a wireless radio air interface, referred to as the Radio Access Technologies (RAT), which utilizes a specific amount of spectrum commonly measured by the transmission bandwidth.
RATs are characterized by the required transmission bandwidth, transmission frame duration, frequency reuse factor between system radio APs, user multiple access scheme, modulation and coding configurations along with the transmission and reception protocols. Due to the limited amount of spectrum available for cellular systems, RATs are typically designed with the objective of enabling maximal spectrum reuse at all system radio APs while having the highest possible spectral efficiency.
In terms of RAT support, UE broadly fall into one of two categories: Single Mode User Equipment (SMUE), capable of utilizing a single RAT only, and Multimode User Equipment (MMUE), capable of utilizing multiple RATs. Multiple RATs are primarily deployed at system radio APs in cellular communication systems to accommodate variations in the capabilities of UE and maintain connectivity of SMUE. Each system radio AP could support one or more RATs and available bands or sub-bands are generally partitioned between RATs when deploying multiple RATs at system radio APs covering the same geographical areas. MMUE also support multiple RATs to maintain UE connectivity when connecting to system radio APs supporting a single RAT or multiple RATs that are inferior to the highest performing RAT supported by the MMUE.
When connecting to system radio APs, UE are typically configured to utilize a single RAT only at any time. Such a mode of operation is referred to herein as Single-Mode Access (SMA). MMUE are thus limited under SMA to utilizing a single RAT even when connecting to system radio APs deploying multiple RATs. When connecting to system radio APs deploying multiple RATs under the restriction of SMA, MMUE are typically configured to utilize the highest performing RAT jointly supported by MMUE and the connecting system radio APs, referred to as the primary mode of operation, and MMUE configuration is typically capable of adapting the utilized RAT as MMUE connect to different system radio APs as well as when the connectivity requirements of user applications change. Nevertheless, configuring MMUE to utilize a single RAT only when connecting to system radio APs deploying multiple RATs can result in the suboptimal utilization of system radiofrequency resources, MMUE capabilities and the capabilities of system radio APs.
When connecting system radio APs utilizing a single RAT over multiple bands, UE may simultaneously utilize (i) all bands jointly supported by UE and connecting system radio APs; or (ii) a subset of bands jointly supported by UE and connecting system radio APs. In the latter case, UE may not utilize all bands jointly supported by UE and connecting system radio APs for various reasons that include, but are not limited to, connectivity requirements of user applications that may not be fulfilled at certain bands or are better fulfilled by other bands, energy efficiency considerations and UE hardware or processing limitations. Traffic split mechanisms include, but are not limited to, sequential and weighted traffic split. Under sequential traffic split, traffic demand is steered at a designated band and traffic demand exceeding the capacity of the designated band is steered at another designated band and so on. On the other hand, weighted traffic split divides traffic between bands based on band capacity, such that bands providing equal capacity would carry equal amounts of traffic.